Furuno 587, interference from outboard motor

[Anonymous]

Hello,

I am looking for suggestions on limiting the interference on the 50kHz side of my 587. It is from the outboard motor, which can be seen in the attached. I was offshore, with the motor off and then fired up the motor for a test, you can see the clutter with gain at AF. The outboard is connected to Bank 1, starting battery and Bank 2 runs the boat electrical accessories. There is a Blue Sea System Mini Add-a-battery system in place which keep both batteries charged with alternator output but isolates the start battery to Bank 1.

The boat is a Fiberglass Parker 21 walk around. The 587 GND terminal on the back of the case is not connected (but in a glass boat, to what? Batt GND?). I was recently told about a GND block (name unknown) which mounts in the area of the bilge/through hulls/transducers. The block is then connected to a through hull with a heavy wire and then the accessory panel GND is connected to the block.

What about filters on the bank 2 battery, on either the input from the Add a Battery system, from the Bank 2 + terminal or at the fuse panel, just before the + supply for the 587, but after the fuse? Are there any known items and is this common noise? I would like to keep the Add a Battery system in place as I run radio, bait bump, GPS, radar, lights etc from bank two and having it topped off is a nice feature.

 

[Johnny Electron]

Noise can be hard to deal with on a boat. Have you ensured that your transducer cable or power cable isn't run along side other wires where noise might couple into the wiring? The noise could be being picked up from the transducer itself if something on the boat is putting out noise in that same freq range. Putting a power filter might help if the noise is coming in with your power. Have you disconnected the transducer and seen if the noise is still there?

 

[Anonymous]

Hello,

I have not disconnected the transducer, but will do so this weekend. To confirm, with the 587 operating normally, yet with interference showing and motor running, if I disconnect the ducer cable and the display shows a clean black screen, then the culprit is noise picked up directly by the ducer or along it's cable run?


The transducer cable is running stern to console along a separate path from the DC power supply and motor harness. The two areas where they come near each other is at the stern, where the ducer cable comes up from the hull and past the area of battery 1. It is routed away from the motor harness and DC cables, but to do this, must pass directly by the battery. The next area is as the cables and harness reach the backside of the dash board area, the DC supply from batt 2 and motor harness come up from an internal rigging tube and the ducer cable passes nearby as both enter the back of the console. In between these two common areas, there is a foot or more of separation between the ducer cable and others. But, to your point, they do come near each other. If this is a culprit, I will attempt to separate the cables by any means necessary. How close is acceptable?

 

[Johnny Electron]

Since the sounder will have an open transducer connection, you will want to put the unit on manual range just it just doesn't jump the screen around. You might see some spikes (normal) but if you still see the noise on the screen like you do now, then the it is coming in via the power lines not the transducer. If the noise clears, then it is coming from the transducer or being coupled onto the transducer cable. If coming in on your DC power then a DC power filter should clear the problem.